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DNA: Forensic and Legal Applications
By Lawrence Kobilinsky Thomas F. Liotti Jamel Oeser-Sweat
John & Wiley SonsCopyright © 2005 John Wiley & Sons, Inc.
All right reserved.
Chapter OneBiochemistry, Genetics, and Replication of DNA
1.1 EVOLUTION OF IDENTIFICATION: FROM FACES TO FINGERPRINTS TO DNA
When a crime has been committed, it is the job of the investigator to reconstruct the events leading up to and during the incident. The investigator will seek information from a number of sources including witnesses, physical evidence, and records.
People are a very good source of information, but their observations and reporting must be carefully evaluated. One can often learn a great deal by questioning the victim's family members, and associates, as well as strangers. Those who come into contact with a criminal suspect may include, among others, witnesses to or the victims of a crime. Investigators can use information obtained from such individuals to recreate the past and to solve a crime mystery. Before modern scientific and technological methods were developed to study physical evidence, this was one of the most important methods for solving crimes. Eyewitness testimony was the best way to identify the perpetrator. Indeed, two eyewitnesses were required to convict a person of a crime under Hebraic law (Deut. 17:6).
When eyewitnesses are lacking, physicalevidence may be the only way to solve a crime. Materials found at a crime scene can be used to link or associate a suspect to it, and the information derived from evidence analysis can be used to exonerate or convict a suspect. Various types of physical evidence can be found at crime scenes. Shoe prints are used to show what type of shoes a suspect was wearing (Bodziak, 1990). Such evidence allows an investigator to identify the shoe as being part of a certain class. As a result, shoes belonging to other classes can be ruled out. For example, if a shoe print found at a crime scene is from a particular brand of sneaker, this might be used to rule out suspects who are known to have been wearing some other brand of sneaker during the time that the crime was committed. Such information can also be used to individualize an item. One refers to a specimen from a known source as an exemplar. The pattern on the sole of a shoe obtained from a suspect, classified as an exemplar, can be matched to the pattern of a plaster cast of a print found at a crime scene (which we refer to as the questioned print). The comparison between exemplar and questioned specimen can result in what is known as a physical match. Experts can analyze the patterns found on the sole and print, and, as with fingerprints, certain distinguishing markings could prove a match, for example, if there is a deep scratch in the sole of the shoe, caused by wear, and the print found at the crime scene exhibits the identical scratch. Such a match is incontrovertible evidence of the origin of the questioned print. The same kind of analysis can be conducted on tire impressions or even on tool marks. Tool marks refer to the markings made on an object when a tool or other instrument is used to gain entry, i.e. to break open a locked closet or window. Another example of a physical match is a sheet of paper or fabric ripped in half. A comparison of the torn ends by microscopic analysis can reveal if the two halves were created from the same sheet. Both torn ends constitute a physical match or perfect fit. In some situations a relatively unique kind of evidence is found that associates a suspect and victim. Several examples follow of evidence that is uniquely important at a crime scene. A relatively rare type of carpet fiber is found on the body of a murder victim, and it is subsequently found to be identical to the fibers of a rug in the bedroom of a suspect. In such a scenario, the fibers become significant associative evidence.
Synthetic or natural fibers are sometimes transferred from person to person upon physical contact, making these forms of trace evidence important. This is an example of the Locard exchange principle described in more detail in Section 3.6.1. When two bodies come into contact, there is an exchange of material between them. Sometimes these materials are so miniscule as to go unnoticed; for example, when extremely small fibers are transferred from victim to suspect or vice versa. If these fibers are somewhat unique, for example, dyed using an unusual chemical compound, they may be useful in linking victim and suspect. The same is true of hair that is easily transferred on clothing from person to person. There are numerous characteristics of evidentiary hair both visual and microscopic that can be used to compare it to known hair specimens taken from a suspect or victim. Hair can also be examined using several DNA (deoxyribonucleic acid) techniques to determine its origin.
The O.J. Simpson prosecution team attempted to link him to the crime scene after one bloody glove was found at the scene and its mate was found behind his house (Schmalleger, 1996). These gloves were easily identified because of the palm vent, stitching, hem, and other characteristics. Nicole Brown Simpson, his former wife and murder victim, had bought him two pairs of these Aris Isotoner Lights, size extra-large gloves in December of 1990, about three and a half years before she was murdered. What makes these gloves even more significant is the fact that there were only about 200 pairs sold that year by Bloomingdales's department store. The defense argued that the pair of gloves in question was unlikely to be Simpson's when O.J. unsuccessfully tried, at the prosecutor's request, to put on the pair of gloves found at the crime scene. Many observers of the trial felt that the prosecution should never have allowed the defendant to take possession of the evidence, thereby allowing him to demonstrate to the jury that the gloves were too small to fit his hands. In fact, some felt that either the gloves had shrunk or that Simpson was trying to show that he could not get them on. Simpson had put on a pair of rubber gloves before trying to put his hands into the evidentiary gloves. This would have made it difficult to put the gloves on even if they actually had fit his hands.
Fingerprints are another type of physical evidence used for human identification and also to link an individual to a location or to a victim (Cole, 2001; Lambourne, 1984; Cowger, 1983; Rhodes, 1956). Fingerprints are impressions made from the papillary ridges on ones fingertips. These epidermal ridges are arranged in very different or unique patterns on each of our fingertips. These patterns do not change from the time of birth until the time of death. Fingerprints provide absolute proof of identity. The science of fingerprint identification is called dactyloscopy. Similar ridges can be found on the palms and on the toes and soles of the foot. Although a print pattern can be described as a loop, whorl, or arch, within each of these configurations, ridges can be arranged in a variety of ways including straight lines with forks that split like forks in a road. In 1880 Henry Faulds and William Herschel discovered that every individual has unique, permanent fingerprint patterns on the tips of his or her fingers. This discovery was subsequently verified by Sir Francis Galton, who proposed a system of fingerprint classification based on the patterns of loops (hairpin ridges), whorls (circular or spiral ridges), and arches (tent or mountain-like ridges). Sir Edward Henry developed a classification system based on the work of Galton. The Henry system of classification was published in 1900 and was used to collect and categorize fingerprints of criminals and is still in use today. Beside the Henry system there is also a widely used system called the NCIC (National Crime Information Center) classification system. The FBI (Federal Bureau of Investigation) classifies a total of eight different fingerprint patterns: (1) plain arch, (2) tented arch, (3) radial loop, (4) ulnar loop, (5) double whorl, (6) central pocket whorl, (7) plain whorl, and (8) accidental whorl.
The most common type of fingerprint pattern is the ulnar loop. Another fingerprint classification system based on Galton's work was introduced by Juan Vucetich, an Argentinian, in 1888, and this system is still used in many Latin American countries.
Although the impression left by the ridges on the ends of our fingertips when we handle objects are not always visible, they can be made visible through chemical enhancement. A fingerprint invisible to the naked eye is called a latent print. Latent prints are usually created upon touching an object or surface and at the same time depositing some naturally secreted or environmentally acquired material onto it. However, after one's finger contacts an object, a perfect fingerprint is not always left (Barnett and Berger, 1977). Sometimes only a portion of the pattern on the edge of one's finger remains; a partial fingerprint can be found in the spot that was touched. Other times no useful print information remains at the point of contact. Fingerprint examiners will compare latent prints to known or exemplar prints by examining specific identification points in the pattern that consist of either dots, islands, ridge endings, or bifurcations (branching of a single ridge into two ridges). Although an inked print can reveal up to 100 such points (minutiae), latent prints may have only a small fraction of these points. Some examiners require at least 7 or 8 identical points before they will state that the latent and exemplar have the same origin. However, there is no specific minimum number that will satisfy all examiners.
In the early 1970s, law enforcement began using computers to classify, store, and retrieve fingerprint data. Today, crime labs have Automated Fingerprint Identification Systems (AFIS) that scan a fingerprint image and convert the minutiae to digital information (Wilson, 1986). The computer also records relative position and orientation of the minutiae and therefore stores geometric data. Computer databases have been created to record the unique imprints of those in the population who have been arrested or who have provided their prints for employment (armed forces or security guards) or gun ownership. Using AFIS, law enforcement agencies have been able to store fingerprint digital data in large databases. Using these digitized files and a powerful search algorithm, prints obtained from new crime scenes can be compared to those of known offenders on file. The computer also determines the degree of correlation of the pattern, location, and orientation of the minutiae. It can compare hundreds of thousands of prints on file in a second or two. AFIS then prepares a list of those prints that come closest to matching the questioned print so that a fingerprint examiner can make the ultimate call of identification or not. In recent years, using fingerprints to run background checks on individuals attempting to gain employment in certain areas such as early childhood teaching has become common.
Forensic DNA testing has emerged as a highly effective way to identify the source of biological evidence with reliability equal to that of fingerprint identification (Neufield and Coleman, 1990). An individual's total genetic composition, in the form of DNA, is referred to as the human genome. Most of the genome is located in the nucleus of a cell, while the remainder is found in the subcellular organelle known as the mitochondrion. Differences in DNA make every individual unique, and that uniqueness can be attributed to differences in certain areas of the human genome. Portions of DNA are invariant from person to person while other portions differ. Most people thinking about an individual's identification will focus on differences in physical appearance such as height, weight, hair color, eye color, skin color, and so forth. However forensic DNA examiners study the differences in the sequence of subunits that make up the DNA molecule. It is known that the difference between two individuals is only 1 in 1000 building blocks. With the human genome consisting of approximately 3.1 billion building blocks, there are about 3.1 million differences in genome subunit sequence between any two persons. The one exception is the DNA of identical twins (or cloned animals), which is identical.
In recent years DNA analysis has been used the same way that fingerprints have been used to link individuals to crime scenes (Kelly et al., 1987; Jeffreys et al., 1985). One advantage of fingerprinting over DNA analysis lies in the fact that even though identical twins have identical genomes, they still have different fingerprints and can easily be distinguished in this way. DNA does not control this trait because the establishment of ridge patterns on the fingertips, palms of the hands, and soles of the feet is a developmental process that takes place as the embryo develops into a fetus and is not a DNA-coded trait, that is, fingerprint patterns are not related to a person's genetic blueprint.
The advantages of DNA analysis over fingerprint analysis are clear. Even if a surface is touched, a useful record of that contact is not always left behind. A latent print requires a suitable surface and certain conditions for a print to remain. As mentioned above, natural and environmentally derived materials present on the fingers result in fingerprints. If a surface is not smooth, or if it is porous, irregular, or rough, it is unlikely that a useful fingerprint can be obtained. If nothing is touched or gloves are worn, discovering any fingerprint whether whole or partial will be virtually impossible. However, DNA can be obtained from a site even if nothing has been touched. A hair fiber with or without its root intact might have fallen from one's scalp, a cigarette butt with saliva (containing epithelial cells) may have been discarded (Hochmeister et al., 1998), or an item of clothing such as a hat or glove worn by a suspect could be discovered. Today, technology is so advanced that exceedingly small amounts of biological substances (blood, semen, saliva, urine, etc.) generated during the commission of a crime can be DNA tested resulting in the identification and conviction of a suspect (Stouder et al., 2001; Erlich, 1989). The one requirement is that there must be a sufficient amount of DNA and that it be in relatively good enough condition to allow testing to be successful.
However, shifts in environmental conditions including high temperature and/or humidity can have an adverse impact on the extraction of high-quality DNA. When DNA becomes fragmented as a result of bacterial or fungal enzymes, it may become so degraded as to render it useless for forensic purposes. This concept is explained in greater detail in Section 3.2.1.
Official records, documents, and databases are a type of physical evidence that can be used in criminal investigation.
Excerpted from DNA: Forensic and Legal Applications by Lawrence Kobilinsky Thomas F. Liotti Jamel Oeser-Sweat Copyright © 2005 by John Wiley & Sons, Inc.. Excerpted by permission.
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Table of ContentsForeword. Preface. Acknowledgements. 1. Biochemistry, Genetics, and Replication of DNA. 1.1 Evolution of Identification: From Faces to Fingerprints to DNA. 1.2 DNA and Heredity. 1.2.1 A Look at DNA from the Outside In. 1.2.2 DNA—The Chemistry. 1.2.3 Unique Sequence and Repetitious DNA. 1.3 DNA Replication. 1.3.1 Replication in the Cell. 1.3.2 Cloning (Gene Amplification). 2. Biological Evidence—Science and Criminal Investigation. 2.1 Crime Scene Investigation—Biological Evidence. 2.1.1 Help the Victim. 2.1.2 Protect the Scene. 2.1.3 Document the Scene. 2.1.4 Search the Scene. 2.1.5 Schematic Drawing Showing Location and Photography of Items of Evidence. 2.1.6 Packaging and Preserving Evidence. 2.1.7 Transport to Laboratory. 2.1.8 Sexual Assault Evidence. 2.1.9 Evidence Handling in the Laboratory. 2.1.10 Report Writing. 2.2 Serology. 2.2.1 Blood. 2.2.2 Semen. 2.2.3 Saliva. 2.2.4 Urine. 2.2.5 Hair. 2.3 Chain of Custody. 3. Forensic DNA Analysis Methods. 3.1 Associative Evidence and Polymorphism. 3.2 Restriction Fragment-Length Polymorphism. 3.2.1 Isolation of DNA. 3.2.2 Quantification. 3.2.3 Restriction Enzymes: DNA Scissors. 3.2.4 Gel Electrophoresis. 3.2.5 Southern Blotting. 3.2.6 Hybridization. 3.2.7 Autoradiography and Visualization of DNA Banding Pattern. 3.2.8 Analysis of RFLP Results. 3.2.9 Probe Stripping from Membrane. 3.2.10 Match Criteria. 3.2.11 Statistics and the Product Rule. 3.3 Polymerase Chain Reaction. 3.3.1 Development and Theory. 3.3.2 Isolation of DNA. 3.3.3 Quantification 3.3.4 Techniques. 3.4 Analysis of Y-Chromosome STRS. 3.4.1 Y-Chromosome Single-Nucleotide Polymorphism Analysis. 3.5 Analysis of Mitochondrial DNA. 3.5.1 The Mitochondrial Genome. 3.5.2 Quantification. 3.5.3 Sequencing. 3.5.4 Interpretation of Sequence Data. 3.5.5 Heteroplasmy. 3.5.6 Statistics. 3.5.7 SNP Analysis of Mitochondrial DNA. 3.6 Problems with PCR. 3.6.1 Contamination. 3.6.2 Degradation. 3.6.3 Sunlight. 3.6.4 Inhibitors. 3.6.5 Allelic Dropout—Null Alleles. 3.6.6 Human Error. 3.7 Underlying Facts and Assumptions in Forensic DNA Testing. 4. Genetics, Statistics, and Databases. 4.1 Human Genetics, Population Genetics, and Statistics. 4.1.1 Power of Forensic DNA Analysis: How Significant Is the Match? 4.1.2 Genetics and Statistics. 4.1.3 Mendel’s Laws of Genetics. 4.1.4 Meiosis. 4.2 Population Genetics. 4.2.1 Hardy–Weinberg Equilibrium. 4.2.2 Subpopulations and Substructure. 4.3 Need for Quality Control and Quality Assurance. 4.4 SWGDAM (Formerly Known as TWGDAM) Standards. 4.5 DNA Advisory Board. 4.6 Mitochondrial DNA and Y-Chromosome STR Analysis and Statistical Calculations. 4.7 Experimental Controls. 4.8 Validation of New DNA Methods. 4.9 Single-Nucleotide Polymorphism Analysis. 4.10 Database Size and Composition. 4.11 DNA Databases. 4.12 Power of Discrimination. 4.13 Mixtures and Statistics. 4.14 Probability of Exclusion. 4.15 Likelihood Ratio (LR). 4.16 Paternity Determinations. 4.16.1 Exclusion of the Alleged Father as the Biological Father. 4.16.2 Inclusion of the Alleged Father as the Biological Father. 4.17 Lab Accreditation, Certification, Reputation, and Facilities. 4.17.1 Quality Control. 4.17.2 Quality Assurance. 4.17.3 Proficiency Testing. 4.17.4 Certification. 4.17.5 Laboratory Accreditation. 4.18 Reviewing a DNA Report—A Sample RFLP Analysis. 4.19 Reviewing a DNA Report—A PCR-Based DNA Examination (HLADQA1, PM, D1S80, and CTT-CSF1PO, TPOX, THO1). 4.20 Reviewing a DNA Report—A PCR-STR-Based DNA Examination (CODIS Loci). 4.21 Reviewing a Paternity Report Based on Analysis of DNA. 5. Litigating a DNA Case. 5.1 Legal Theory. 5.1.1 Admissibility of Scientific Evidence: A Primer. 5.1.2 Common Law and The Creation of a Judicial Gatekeeping Function. 5.1.3 Federal Rules of Evidence and the Expansion of the Judicial Gatekeeping Function. 5.1.4 Daubert: The Supreme Court Sets Forth a Standard. 5.1.5 General Electric Company et al. v. Joiner et ux. 5.1.6 Kumho Tire: The Court Continues Its Expansion of the Judicial Gatekeeping Function. 5.1.7 Judicial Gatekeeping Function and Its Evolution in New York State. 5.2 Admissibility of DNA Evidence. 5.2.1 PCR-STR DNA Evidence. 5.2.2 Mitochondrial DNA. 5.2.3 Animal DNA. 5.2.4 Plant and Viral DNA. 5.2.5 Statistics. 5.2.6 Paternity. 5.3 Legal Practice. 5.3.1 Different Stages of a Trial. 5.4 DNA for Defense Attorneys—Contesting DNA Evidence. 5.5 DNA for Prosecutors. 5.6 DNA for Judges. 6. DNA Evidence at Trial. 6.1 Attacking and Defending DNA Evidence. 6.1.1 Theory of the Case/Plan of Attack. 6.1.2 What is Required for DNA Test Results to be Admitted into Evidence? 6.2 DNA for the Prosecutor or Those Who Seek to Admit DNA Evidence. 6.2.1 Effective Admission of DNA Evidence Takes Place in Three Stages. 6.3 DNA for the Defense or Those Who Seek to Mitigate the Effect of DNA Evidence. 6.3.1 Preventing the Admission of DNA Evidence in Part or in Its Entirety. 7. Exonerating the Innocent through DNA. 7.1 Postconviction Appeals Based upon DNA Evidence. 7.2 Postconviction DNA Testing: Recommendations for Handling Requests. 7.2.1 Role and Response of the Prosecutor. 7.2.2 Role and Response of the Defense Attorney. 7.3 Legal Standards Governing Postconviction Testing. 7.3.1 Argument for a Constitutional Right to Postconviction DNA Testing. 7.3.2 Other Non-Postconviction Testing Statute Arguments. 7.4 Postconviction DNA Testing Statutes. 7.5 Preventing Postconviction DNA Testing through Waiver. 7.6 The Future of DNA Technology. Appendix A: Bibliography: Selected by Topic Area. Appendix B: Cases Involving the Admissibility of DNA Evidence. Appendix C: Information Pertinent to Attempts to Overturn Convictions Based Upon DNA Evidence. Appendix D: Offenses in New York State Resulting in Mandatory DNA Testing for Database Inclusion. Appendix E: Postconviction DNA Testing, Preservation of Evidence and Compensation for Wrongful Convictions: Relevant Legislative Information. Appendix F: Items Obtained through Discovery. Appendix G: Glossary. Index.
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"DNA: Forensic and Legal Applications is a comprehensive and invaluable guide to the field, covering topics ranging from collecting samples in the field to presenting the complex results to a jury. We are sure that it will play its part in promoting this most powerful tool in the forensic scientist’s armamentarium." —From the Foreword by Drs. James Watson and Jan Witkowski